In general, many systems and methods processing hydrocarbon-containing fluid, in particular for liquefying hydrocarbon-comprising gas, are known. Often, an input fluid flow is used that comprises a highly purified gas. Often, such an input fluid flow is already dried, i.e., water vapour has been removed. Furthermore, often additionally carbon dioxide has been removed in a separate stage.
In many cases, however, the origin of a gas that needs to be liquefied has many sources. For instance, natural gas may originate from different wells. Another example is biogas, which usually has many different additional compounds in addition to methane.
U.S. Pat. No. 2,900,797 in 1959 already described the separation of normally gaseous acidic components and normally gaseous hydrocarbons. According to its description, in one aspect this invention relates to the purification of a methane stream containing carbon dioxide. In another aspect this invention relates to the removal of carbon dioxide from natural gas. Various normally gaseous hydrocarbon streams that contain methane as the major component also contain normally acidic components, such as carbon dioxide, in amounts which require the separation of such normally gaseous acidic components from the gas stream. It was found that operating a process according to this publication in practise was complex.
WO2014166925 of 2013 according to its abstract describes a method of liquefying a contaminated hydrocarbon-containing gas stream, the method comprising at least the steps of:
(a) providing a contaminated hydrocarbon-containing gas stream;
(b) cooling the contaminated hydrocarbon-containing gas stream in a first heat exchanger thereby obtaining a cooled contaminated hydrocarbon-containing stream;
(c) cooling the cooled contaminated hydrocarbon-containing stream in an expander thereby obtaining a partially liquefied stream;
(d) separating the partially liquefied stream in a separator thereby obtaining a gaseous stream and a liquid stream;
(e) expanding the liquid steam obtained in step (d) thereby obtaining a multiphase stream, the multiphase stream containing at least a vapour phase, a liquid phase and a solid phase;
(f) separating the multiphase stream in a separator thereby obtaining a gaseous stream and a slurry stream;
(g) separating the slurry stream in a solid/liquid separator thereby obtaining a liquid hydrocarbon stream and a concentrated slurry stream;
(h) passing the gaseous stream (80) obtained in step (d) through the first heat exchanger thereby obtaining a heated gaseous stream; and
(i) compressing the heated gaseous stream thereby obtaining a compressed gas stream; and
(j) combining the compressed gas stream obtained in step (i) with the contaminated hydrocarbon-containing gas stream provided in step (a).
The field is thus fully in motion and still seeking for process optimization.
Often, systems for liquefying gas, in particular gas comprising a large amount of methane, are designed for operation at a large industrial scale. Biogas, for instance, is usually produced in a decentralized way. Thus, there is in particular need for a gas treating and liquefying system that that offers freedom of design, in particular as to scale of design.